1. Field of the Invention
The present invention relates to an apparatus and method for detecting a tracking error signal. More particularly, the present invention relates to an apparatus and method for digitally detecting a tracking error signal using multiple phase clocks.
2. Description of the Related Art
Optical disk recording reproducers may reproduce data recorded in optical disks, e.g., compact discs (CD), digital versatile discs (DVD), etc., by restoring radio frequency (RF) signals from the optical disks. More specifically, optical disk recording reproducers may irradiate light onto optical disks, detect reflected light with detectors, e.g., photodiodes (PD), generate RF signals from the detected light, and divide the generated RF signals according to a predetermined level to restore data.
Optical disk recording reproducers may also detect tracking errors so as to exactly track optical disks. Optical disk recording reproducers may detect tracking error signals using reflected light, and may correct tracking errors using tracking error signals. Differential phase detection (DPD) may be used to detect tracking error signals.
FIG. 1 illustrates a block diagram of a conventional apparatus 100 for detecting a tracking error signal. Referring to FIG. 1, the apparatus 100 for detecting the tracking error signal may include gain controlled amplifiers GCAA, GCAB, GCAC, and GCAD 110, equalizers EQA, EQB, EQC, and EQD 120, comparators CMPA, CMPB, CMPC, and CMPD 130, voltage controlled phase shifters VCPSA, VCPSB, VCPSC, and VCPSD 140, phase detectors PDAB and PDCD 150, a subtractor SUB 160, and a low pass filter (LPF) 170.
The apparatus 100 for detecting the tracking error signal may receive signals output by a photo detector (not shown). The photo detector may convert four divided lights into electrical signals MA, MB, MC, and MD. The gain controlled amplifiers 110 may receive the electrical signals MA, MB, MC, and MD, and may output differential signals AP and AN, BP and BN, CP and CN, and DP and DN, having opposite phases, respectively, through the equalizers 120, respectively, in which intensity variations of the differential signals AP and AN, BP and BN, CP and CN, and DP and DN, may be corrected according to differences in amplitude of vibrations and pit lengths.
The comparators 130 may compare the differential signals AP and AN, BP and BN, CP and CN, and DP and DN, and may extract phases A, B, C, and D. The voltage controlled phase shifters 140 may control values of the phases A, B, C, and D. The phase detectors 150 may detect phase differences using the phases A, B, C, and D having controlled values.
Among the detected phase differences, two phase differences, e.g., A and C, and B and D, may be respectively added. The subtractor 160 may receive the two added phase differences, and may subtract the two added phase differences, e.g., subtract B+D from A+C. The LPF 170 may remove ripple and noise of the subtracted signal, thereby producing a tracking error signal DPD_TE.
Since a width of a phase error is reduced as a disk speed increases, the apparatus 100 may require a clock having a high frequency, so as to directly count phase differences. However, there may be a limit as to how high a clock frequency may be realized in a given system.
Also, when receiving high frequency signals, the apparatus 100 may use an analog method based on pulse width modulation (PWM) integration to extract phase errors. When the apparatus 100 detects the tracking error signal using PWM integration, a digital-analog converter that generates a control voltage may be needed for the voltage controlled phase shifters VCPSA, VCPSB, VCPSC, and VCPSD 140. When the phase differences are output as PWM signals, an analog passive filter that converts PWM signals into analog signals may be needed.
Optical disk recording reproducers may be digitized and integrated as a system on chip (SoC). Thus, digitization of the apparatus 100 may be required for optical disk recording reproducers.
However, as noted above, when the apparatus 100 uses PWM integration, a digital-analog converter and an analog passive filter are needed. Also, since the tracking error signal has a low frequency, the apparatus 100 for detecting the tracking error signal needs a high level LPF that generates the low frequency tracking error signal. Since it is difficult to digitize the digital-analog converter, the analog passive filter, and the high level LPF, it is very difficult to realize the apparatus 100 for detecting the tracking error signal as a digital circuit or SoC.